Electrical apparatus



April 2, 1 v R. E. MENTZER 3,084,237

ELECTRICAL APPARATUS Filed Nov. 14, 1960 INVENTOR. 067 975. 4/54 7254United States Patent O 3,084,237 ELECTRICAL APPARATUS Robert E. Mentzer,Southampton, Pa., assignor, by mesne assignments, to PhilcoCorporation;Philadelphia, Pa., a corporation of Delaware Filed Nov. 14,1960, Ser. No. 68,980 4 Claims. (Cl. 200-122) This invention relates toelectrical apparatus and more particularly to apparatus for regulatingvoltages. While of broader applicability, apparatus of the presentinvention has particular utility in the field of electronic equipmentsuch, for example, as television receivers.

In the design of television receivers an important factor to beconsidered is the variation in line voltage to which a receiver issubject in the normal operation thereof. For example, the line voltagein a particular location characteristically varies between 105 and 130vol-ts. This variation of course necessitates the use of componentscapable of efficient operation within the range of such voltage values,as well as the provision of voltage control means for other componentsnot readily adaptable to wide voltage variations. A particular exampleof such components as the latter are the electron tube filamentcircuits, wherein excessive voltages applied thereto producedeterioration of the tube filaments as well as premature vaporization ofelectron emissive surfaces of the cathode of the cathode ray tube.

The problem of voltage variations has been met by inclusion of voltageregulation devices comprising switch means provided with a bimetallicactuator arm operated by a resistance heater associated therewith andenergized by the line voltage being controlled. Such devices, whilehelpful, have not provided a complete solution to the problem. Theswitch heater of the regulatory device is subject to unregulated powerthroughout its warmup interval and, in the event low voltage occurs atthis time, the switch arm may undesirably delay movement of its contactto energize the electron tube filaments, and consequently unduly delayoperation of the TV receiver.

It is therefore an objective of the invention to provide simple andeffective improved voltage control apparatus overcoming the abovedescribed difliculties.

It is a particular objective of the invention to provide a thermallyactuatable switch adapted for use in a variety of voltage control means.

It is still another object of the invention to provide an improvedelectro-mechanical device of the type utilizing a bimetallic element.

In accordance with the foregoing and other objectives the inventioncontemplates use of a temperature compensated bimetallic switchactuating element so thermally associated with a heaterelementenergizable by a voltage source to be controlled-as to providepredetermined time delay operation of the switch. The bimetallic switchactuating element includes a flexible and resilient birnetal stripanchored rigidly toward one end to suitable support means and biasedtransversely by a force applied to the strip in a region of its freeend. According to one aspect of the invention a switch contact isdisposed on the strip in a region intermediate the anchored end and theportion of the strip to which the initial flexing force is applied.

According to another embodiment of the invention initial flexing of thestrip is achieved by applying the required force through a second pairof electrical contacts operably coupled with a second heater associatedwith the strip.

The manner in which the foregoing objects and advantages of theinvention may best be achieved will be more fully understood from aconsideration of the following 3,084,237 Patented Apr. 2, 1963 detaileddescription taken in light of the accompanying drawing, in which:

FIGURE 1 is a perspective showing of one form of thermally responsiveswitch made in accordance with the inventionand including a somewhatdiagrammatic showing of electrical circuitry adapted for use therewith;

FIGURES 2, 2A, 2B and 2C are diagrammatic showings of operationalfeatures of the thermal switch shown in FIGURE 1;

FIGURE 3 is a showing similar to FIGURE 1, but illustrating another formof switch made in accordance with the invention and including adiagrammatic showing of electrical circuitry adapted for use therewith;and

FIGURES 4, 4A, 4B and 4C are diagrammatic showings of operationalfeatures of the embodiment of the invention shown in FIGURE 3.

Referring now to the drawings, and particularly to FIGURE 1, abimetallic element 10 comprises a pair of flexible and resilient legs orstrips 11 and 12 interconnected by a transverse portion 13. Element 10is mounted upon an insulative base 14 by a rivet 15 extending throughthe base and the free end portion of leg 11. Leg 11 extends slightlyupwardly and away from base 14 so as to space transverse portion 13 andthe other leg 12 from the base as shown.

Strip or leg 12 has affixed to its lower surface an electrical contact16 disposed intermediate the free end of leg 12 and the transverseeportion 13. An adjustable stop member 18 is disposed upon base 14 andforcibly engages the free end of strip 12, applying force thereagainstin an amount sufficient to bow the strip concavely upwardly as shown andposition contact 16. Adjustment of stop member 18 is achieved by setscrew 19 supported by insulative base 14. Stop member 18 includes a fiatspring portion 20 mounted also upon base portion 14 by rivet 15, andadapted to bias set screw 19 in any of its adjusted positions, and anelectrically nonconductive stop 21 disposed between strip 12 and springportion 20. While strip 11 provides temperature compensation for strip12 up to contact 16, the biasing spring 20 is of such material as toprovide temperature compensation for the portion of strip 12 betweencontact 16 and its free end.

An additional electrical contact 22 is mounted on the base beneathcontact 16 carried by strip 12, contact 22 being disposed and adaptedfor engagement by contact 16 in response to flexing movements of strip12, as will hereinafter be more fully explained. Electrical contact 22is mounted upon base 14 by means of a flat spring 31 aflixed to thelatter by a rivet 32. Relative positions of contacts 16 and 22 are alsoadjustable by a set screw 33 mounted in the base and engaging the end ofspring 31, the latter being disposed and adapted to bias the set screw33 in any of its positions.

A resistance heater 23 is wound about strip 12, and is thermally coupledto the latter while being so constructed and arranged as not tointerfere with flexing movements of the strip. One end of heater 23 isconnected to a voltage source L, through a switch 27, and the other endof the heater is connected to electrically conductive strip 12 ofbimetallic element 10 as seen at 24. One side of a thermistor 25 also iselectrically connected to heater 23 through rivet 15 and element 10, andthe other side of the thermistor is connected in series with an electrontube filament string designated generally by the numeral 26. Filamentstring 26 is connected at its other end to line L. Thus, heater 23,thermistor 25, and filament string 26 are in series circuit with line L,as shown in FIGURES 1 and 2.- Contact 16 is electrically connected tostrip 12 and its mating contact 22, on spring 31, is connected throughrivet 32 to a point of interconnection between thermistor 25 andfilament circuit 26.

' flexing movement of strip 12 is in the nature of bending about stopmember 18 as best shown diagrammatically in FIGURE 2A. Additionalflexing of strip 12 moves it to the position shown in FIGURE 2B, andfinally to the position shown in 2C. Flexing of strip 12 through thestrip 34 mounted upon base 14a by a rivet'35. A temperature-compensatingextension 34a of strip34 carries contact 21a. Contact 22a is disposed indirect electrical contact with strip 34, whereas contact 21a isinsulated from extension 340' by electrically non-conductive spacer 21b.Biasing of strip 12a is provided by a set screw 36 carried by the baseand which screw is biased by spring 34. Temperature compensation for thestrip 12a successive positions seen in FIGURES 2, 2A, 2B and 2C isbrought about by increased heating of bimetallic strip 12 by heater 23.

A still better understanding of the invention will be had from adetailed explanation of the operation of the hereinabove describedembodiment. Closing of switch 27, to energize the filament circuitry 26shown by way of example as the load, causes current to fiow through thebimetal heater 23, thermistor 25, and filament string 26. Since theresistance of thermistor 25 is characteristically relatively high uponfirst energizing the circuit, the initial current through the filamentstring 26 and through heater 23 is held to a relatively low value.Consequently initial high surges of current are prevented by thethermistor from flowing through the filaments until such time as thebimetal regulatory switch can come up to its operating temperaturerange. As the thermistor warms, its resistance decreases permitting ahigher current to flow therethrou-gh, and also through the heater 23 andfilaments 26. As heater 23 receives more current it heats bimetal strip12 sufficiently to flex the same to the position shown in FIGURE 2A,closing contacts 16 and 22 thereby shunting thermistor 25 from thecircuit. Continued energization of heater 23 causes the free end ofstrip 12 to flex upwardly thereby disengaging the said end from stopmember 18 (FIGURE 2B). Thereafter any increase in current due toexcessive surges of voltage will cause the bimetal strip 12 to curlfurther and reopen contacts 16 and 22 (FIGURE 2C), thereby placingthermistor 25 again in the circuit as protection. As the surge subsidesstrip 12 returns to the position shown in FIGURE 28, closes contacts 16and 22 again shunts thermistor 25.

By virtue of this novel bimetallic switch arrangement a thermistorserves the combined functions of a voltage surge protector and regulatorresistor. Once operating as a voltage regulator, it is seen that thefree end of bimetal strip 12 is clear of engagement with the stop member18 and plays no part in the operation of the device. As the line voltagedrops at L, and the current flowing through filaments 26 decreases, thecontacts will permanently open at some current value significantly lowerthan the selected minimum operating current of filaments 26.

Use of the above described bimetallic structure advantageously providesfilament surge protection, as well as regulation, because during theinitial warm-up interval the surge current is reduced by the thermistorin series with the filaments. After the initial warmup interval, thethermistor assumes a low resistance value and is switched in and out ofthe series circuit by the bimetallic switch, thereby maintaining thefilament current at an average value.

In the embodiment of the invention shown in FIGURES 3 to 4C, bimetaldevice 104 is substantially the same as that illustrated in FIGURES 1 to2C, being comprised of mounting strip 11a, movable strip 12a,interconnecting portion 13a, insulative base 14a and a rivet 15amounting strip 11a to base 14a. Electrical contacts 16a and 17a areprovided on electrically conductive strip 12a each contact beingdisposed upon the lower side of the strip and opposite respectivecontacts 22a and 21a provided upon base 14a. Contact 22a is carried by aresilient conductive up to contact 16a is provided by strip 11a whiletemperature compensation for the portion of strip 12a between contacts16a and 17a is provided by strip 340. v

A heater 23a is thermally associated with strip and is electricallyconnected to the latter as seen at 24a. A second heater 30 is thermallyassociated with strip 12a.

Strip 12a is connected to one side of line L through the agency ofinterconnecting portions 13a, strip 11a, and resistor R. Heater 30 isdisposed for connection across line L in series electrical circuitrywith line switch 27a, contacts 21a, 17a, strips 11a, 12a, 13a andresistor R. Heater 23a is disposed for alternate connection across lineL either in series electrical circuitry with switch 27a, filament string26a, strips 11a, 12a, 13a, and resistor R, or in series electricalcircuitry with switch 27a, filament string 26a, strip 12a and contacts16a, 22a. Bimetal dcvice 10a as shown is used to control, as will behereinafter more fully explained, voltages applied to filament string26a of a television receiver (not identified), filament string 26a beingdisposed in circuitry hereinabove described and energized by line L.

Referring now with particularity to FIGURES 4 to 4C, the bimetal strip12a is initially flexed to assume the position diagrammatically shown inFIGURE 4 wherein contacts 16a and 22a are open and contacts 17a and 21aare closed. Upon closing switch 27a to energize the circuitry, it willbe seen that boost heater 30, filament string 26a, heater 23a andresistor R are energized immediately. As strip 12a is rapidly heated itis flexed to the position shown in FIGURE 4A to close contacts 16a and220. This shunts out resistance R and energizes filament string 26a andheater 23a to a higher power level. Shortly thereafter strip 12acontinues to flex or curl to the position shown in FIGURE 43, wherein itis seen that contacts 17a and 21a are opened and boost heater 30deenergized while operating heater 23a and filament string 27a remainenergized. Note that resistor R is shunted out due to its parallelcircuitry with contacts 16a, 22a. In this position of the switch means10a any excessive increase of voltage effects increased heating ofheater 23a and causes the strip 12a to flex still further to theposition shown in FIGURE 4C, which disposes resistance R in series withfilament string 26a and heater 2311, thereby reducing the power suppliedto the filament string and heater. As a result of the reduction in powersupplied to the heater, the strip 12a returns to the position shown inFIGURE 43, whereupon contacts 16a and 2211 again close and resistor R isdeenergized, increasing the power to the heater and filaments. Thiscycle is repetitive in nature and provides a desired regulated averagepower supply to the filament string. In the event of extreme voltageapplied through line L, the switch will remain in the position shown inFIGURE 4C.

It will be therefore understood that by the latter embodiment of theinvention there is advantageously provided means associated with thebimetallic strip which ensures overcoming the thermal inertia of theprotective device 10a upon closing of switch 27a. Thus the desiredprotection of the filament string 26a is afforded almost immediatelyupon energization of the circuitry.

From the foregoing description of the two illustrated embodiments of theinvention it will be understood that there is achieved differentialmovements of a bimetallic element whereby one or more switchingfunctions are provided, by a single such element, and the samebimetallic device may be used in different circuits for differentpurposes. In this regard it is pointed out that the bimetallic switch asshown in FIGURES 3 and 4 to 4C, may be used in the circuitry shown inFIGURES 1 and 2 to 2C, in which event outer contacts 17a, 21a would notbe used but would function only as a stop member.

I claim:

1. In thermally actuatable switching apparatus: a bimetalliccurrent-carrying strip affixed to supporting means toward one endthereof and adapted to flexabout said one end in response to temperaturechanges; first and second heater elements thermally associated with saidstrip; and contact means electrically associated with said heaterelements and operative by said strip as it is flexed, said first heaterelement being energizable initially with said second heater element toheat said strip to its operating temperature, said first heater elementthereafter being deenergizable upon initial flexing of said strip, thestrip thereafter being thermally actuatable by said second heaterelement alone to open and close said contact means.

2. In thermally actuatable switching apparatus: a bimetalliccurrent-carrying strip affixed to supporting means toward one endthereof and adapted to flex about said one end in response totemperature changes; first contact means disposed in forcible engagementwith said strip initially to flex the latter in the direction of flexinginduced by increasing temperature; second electrical contact meanscarried by said strip intermediate its supporting means and said firstcontact means; and first and second electrical heater means thermallyassociated with said strip and initially operative together to raise thetemperature of the strip to flex the same and sequentially to move saidsecond contact means in one direction, while said strip is flexed todisengage it from said first contact means, said first heater means andsaid first contact means being so electrically connected that therecited strip movement deenergizes said first heater means, said secondelectrical heater means being operative thereafter to flex said strip tomove said second contact means in the direction opposite to its recitedfirst movement.

3. Electrical circuit means for effecting a predetermined time delay forthe energization of a filament of an electron tube or the like and forproviding surge protection thereafter, said circuit means comprising: asource of energy; a bimetallic current-carrying strip supported incantilever fashion, said strip being adapted to flex about its supportin response to temperature changes; stop means disposed and adapted toengage said strip and initially to flex the same in the direction offlexing induced by increasing temperature; electrical contact. means forsaid strip disposed intermediate the support for the same and said stopmeans; an electrical resistor; an electrical heater disposed in thermalexchange relation with the bimetallic strip, said heater, said resistorand said filament being disposed in series electrical circuit with saidsource of energy when said bimetallic strip is in its initially flexedposition in which its contact means is open, the construction andarrangement being such that, sequentially, upon initial heating of saidstrip by said heater, said contact means is moved to closed positionwhereby said resistor is shunted out of the circuit and there isprovided a series electrical circuit comprising the electircal heaterand the tube filament, and upon continued heating of said strip saidcontact means is moved to open position, in the opposite direction, withaccompanying disengagement of said strip from said stop means, wherebysaid resistor is again placed in series electrical circuit with saidsource of energy, said heater, and said tube filament.

4. Electrical circuit means for effecting a predetermined time delay forthe energization of a filament of an electron tube or the like, and forproviding surge protection thereafter, said circuit means comprising: asource of energy; bimetallic current-carrying strip means fixed tosupporting means toward one end and free to move at the other end inresponse to temperature changes; first and second electrical heatersoperatively associated with said bimetallic strip means; a firstelectrical contact carried in the region of the free end of said stripmeans operative to control circuit means including said first heaterupon movement of said strip means in response to operation of said firstand second heaters; a second electrical contact carried by said-stripmeans intermediate the ends thereof and operative to control saidcircuit means upon movement of said strip means in response to operationof said second heater; an electrical resistor disposed in serieselectrical circuit with said source of energy, said strip means, saidfirst electrical heater, and said first electrical contact, and saidsecond electrical heater being disposed in series electrical circuitwith said electron tube filament, said strip means, and said resistor,the construction and arrangement being such that upon energization ofsaid circuit means saidfirst electrical contact is closed and saidsecond contact is opened whereby a parallel electrical circuit isenergized, one side thereof comprising said second electrical heater,said tube filament, and said resistor, and the other side thereofcomprising said first electrical heater, said strip means, and saidresistor,

continued energization of said circuit effecting opening of said firstcontact and closing of said second electrical contact, whereby only saidone side remains energized.

2. IN THERMALLY ACTUATABLE SWITCHING APPARATUS: A BIMETALLICCURRENT-CARRYING STRIP AFFIXED TO SUPPORTING MEANS TOWARD ONE ENDTHEREOF AND ADAPTED TO FLEX ABOUT SAID ONE END IN RESPONSE TOTEMPERATURE CHANGES; FIRST CONTACT MEANS DISPOSED IN FORCIBLE ENGAGEMENTWITH SAID STRIP INITIALLY TO FLEX THE LATTER IN THE DIRECTION OF FLEXINGINDUCED BY INCREASING TEMPERATURE; SECOND ELECTRICAL CONTACT MEANSCARRIED BY SAID STRIP INTERMEDIATE ITS SUPPORTING MEANS AND SAID FIRSTCONTACT MEANS; AND FIRST AND SECOND ELECTRICAL HEATER MEANS THERMALLYASSOCIATED WITH SAID STRIP AND INITIALLY OPERATIVE TOGETHER TO RAISE THETEMPERATURE OF THE STRIP TO FLEX THE SAME AND SEQUENTIALLY TO MOVE SAIDSECOND CONTACT MEANS IN ONE DIRECTION, WHILE SAID STRIP IS FLEXED TODISENGAGE IT FROM SAID FIRST CONTACT MEANS, SAID FIRST HEATER MEANS ANDSAID FIRST CONTACT MEANS BEING SO ELECTRICALLY CONNECTED THAT THERECITED STRIP MOVEMENT DE-